I had a couple of 504 plans set up for my son at different times when he injured himself.
I called the school and spoke with the vice principal and asked how to do it and he helped set it up
I needed to have a note from the doctor specifying what was wrong and submit that to the school nurse.
I needed to decide what to ask for; in one case it was busing home from school because he had a leg injury, as well as an elevator pass so he did not have to walk up stairs. The school also assigned someone to help carry his books while he was on crutches and moved his locker to a more central place which was situated nearer to his classes so he didn't have to walk that far to get his things. He was also excused in the event he was late to class because he was walking slowly with the crutches. (it was a large school) In the other case he broke his right hand the week before midterms senior year and I was able to ask for someone to sit with him while administering the midterms and writing down his answers. In both situations the 504 was set up in a day and the school was very helpful. It is a federal law and they are required to do this.
I don't know how it is in your state or whether this is a federal law also, but in ours if a child is seriously ill they are entitled, if they go to public school, to have home instruction provided by the district. So in the case that your daughter needs to be refed and cannot be in school, that might be an option to look into if she is well enough to participate in some tutoring either at home or through online classes.
Home instruction is the provision of one-to-one or small group instruction in the student’s place of residence or other appropriate setting due to a health condition, or need for treatment.
So depending on what you think your daughter could benefit from, 504 accommodations could range from:
Your daughter being excused from class and not penalized for any late homework or missed tests due to having doctor's appointments or coming late to school because she is not eating breakfast fast enough, and given the opportunity to make up any missed work.
Excusal from gym
Excusal from health class if they are doing any subject matter concerning "healthy" eating.
Supervision during lunch, perhaps eating lunch with the nurse in her office. You would want to discuss with the nurse what the supervision includes.
Does it include someone getting her a lunch from the cafeteria so that she does not pick out the food herself? Or you dropping off her lunch with the nurse in the morning so she doesn't have any opportunity to throw part of her lunch away? Then sitting with her until it is finished. And you might want to ask that if she doesn't finish her lunch that she needs to sit until it is finished and not be penalized for any classroom time missed.
Hope this helps! And wow your school starts early! Ours doesn't usually start until after labor day.